Pressurized insulant of solid and fluid for a conductor

ABSTRACT

Electrical equipment has a conductive member surrounded by an insulant. The insulant comprises finely divided particles of a solid insulating material in an insulating fluid, which fluid acts as a discharge suppressant and is effectively in the form of a thin film. Means are provided for maintaining the fluid above atmospheric pressure and for maintaining the interparticle pressure.

1451 Oct. 29, 1974 United States Patent 1.191

Burton PRESSURIZED INSULANT OF SOLID AND L. R R R X S l 5 5 F 322 l 4 44 7 7771 7 l l l l t n n 7 H n H 6 cmnmm H 1 C h 85 d k n n w 0 0 h h aM .IOOM VJ T 6 4 5 l 2 5 6 6 7 7 9 9 9 9 9 l l l l l 9 0 oo 9 6 l U 7 76 9 3 0 0 7 ,52 1 4 l 9 0 6 5 0 0 7 7 1 3 2 3 3 3 3 FLUID FOR ACONDUCTOR [75] Inventor: Edward Arthur Burton, Guildford,

England [73] Assignee: Dielectrics International Limited,

174/25 G 174/25 G 174/25 R London, England [22] Filed: Feb. 12, 1973[2]] Appl. No.: 331,775

SPRING MEMBER D E N m S N E T lNSULANT (FLUID+ SOLID) STRANDED CONDUCTORI 11 17 1 13 INSULANT (FLUID+$0LID) 11 Claims, 3 Drawing Figures 2 41p-31t1f FLUID sulating fluid, which fluid acts as a dischargesuppressant and is effectively in the form of a thin film. Means areprovided for maintaining the fluid above atmospheric pressure and formaintaining the interparticle pressure.

Zb pazssuinzen ILE E MEMBRANE 2 8/FILTER IMPERMEABLE IMFERMEA MEMBRANSTRANDED CONDUCTOR EXPANSION DEVICE IMPERMEABLE MEMBRANEBennett................................. Vogel..........Atkins0n...............................

References Cited UNITED STATES PATENTS IN SULANT SPRING MEMBERPRESSURIZED INSULANT OF SOLID AND FLUID FOR A CONDUCTOR BACKGROUND OFTHE INVENTION SUMMARY OF THE INVENTION According to this invention thereis provided electrical equipment comprising a conductive membersurrounded by an insulant. The insulant comprises finely dividedparticles of a solid insulating material in an insulating fluid, whichfluid acts as a discharge suppressant and is effectively in the form ofa thin film. Means are provided for maintaining the fluid aboveatmospheric pressure and for maintaining the interparticle pressure.

The solid insulating material may be quartz, fused silica or mica forapplications requiring a low permittivity insulant or glass or porcelainfor applications permitting a higher permittivity insulant.

The fluid may be either liquid or gaseous and suitable fluids are, forexample, low viscosity mineral oil, fluorocarbon oil, and silicone oil.Suitable gases are, for example, nitrogen and sulphur hexafluoride.

The electrical equipment may have at least two conductive members spacedapart from each other, the space between the conductive members beingfilled by the insulant.

The electrical equipment may, for example, be a cable, a supertensionbushing, a straight joint, a stop joint, a sealing end, a metal cladsupertension busbar, or a super-tension current transformer.

The provision of means for maintaining the fluid above atmosphericpressure and for maintaining interparticle pressure is important if thehighest electrical strengths are to be obtained.

A cable in accordance with this invention may comprise a stranded hollowconductor intended to be filled with the fluid, which acts as adischarge suppressant, above atmospheric pressure, a permeable membranewhich surrounds the conductor, and an impermeable membrane whichsurrounds the permeable membrane, the space between the permeable andimpermeable membranes containing particles of the solid insulatingmaterial and being intended to receive the fluid, which acts as adischarge suppressant, through the permeable membrane, the means formaintaining the fluid above atmospheric pressure and for maintaining theinterparticle pressure surrounding the impermeable membrane.

Suitably the means for maintaining the fluid above atmospheric pressureand for maintaining interparticle pressure comprises a furtherimpermeable membrane which surrounds the first mentioned impermeablemembrane, the space between the impermeable membranes being intended tobe filled with fluid under pressure.

Alternatively the means for maintaining the fluid above atmosphericpressure and for maintaining interparticle pressure comprises metal tapeunder tension wound around the impermeable membrane.

Each particle, is of course, in contact with ticles.

A bushing in accordance with this invention may comprise a conductorsurrounded by a casing, and a corona shield of sheet material whichsurrounds the central part of the conductor and is secured to the casingso as to define a space which is filled with the fluid, which acts as adischarge suppressant, above atmospheric pressure, the remainder of thespace within the casing being filled with the said insulant, there beingformed a passage permeable to the said fluid but not to the particles ofinsulating material between the first mentioned space and the remainderof the space within the casing.

DESCRIPTION OF THE DRAWINGS Embodiments of this invention will now bedescribed, by way of example only, with reference to the accompanyingdrawings of which:

FIG. I is a sectional view of a first supertension cable in accordancewith this invention;

FIG. 2 is a sectional view of a second supertension cable in accordancewith this invention; and

FIG. 3 is a longitudinal sectional view of a supertension bushing inaccordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1 the cableshown therein has a stranded conductor 1 which is hollow, the duct 2formed within it being filled with mineral oil under pressure. It willbe appreciated that oil from the duct 2 can pass through the strandedconductor 1. Suitable conducting or semiconducting filter paper, e.g.carbon paper tape, is wound onto the conductor 1 to form a layer 3 whichacts as a membrane permitting passage therethrough of mineral oil. Aconcentric impermeable membrane 4 surrounds the layer 3 of carbon papertape, the space in between the membrane 4 and the layer 3 being filledwith an insulant 5 which comprises particles of a solid insulatingmaterial in mineral oil. The membrane 4 is surrounded by a furtherimpermeable membrane 6 and the space between the membranes 4 and 6 isfilled by a fluid 7 under pressure.

As the membrane 3 is permeable, the mineral oil in the duct 2 exerts apressure on the insulant 5, say the pressure P,. The pressure of thefluid 7 in the space formed between the membranes 4 and 6 also acts onthe insulant 5 at a pressure of, say, P so that the net pressure actingon the insulator 5 is P P The cable may be manufactured by extruding asuitably wetted powdered solid insulating material within the spacebetween the layer 3 and the membrane 4 and mineral oil is then suppliedunder pressure to the duct 2 and passes through the layer 3 into thepowdered insulating material to form the insulant 5.

The cable shown in FIG. 2 is similar to that shown in FIG. 1 and onlythe differences will be explained. In this cable the impermeablemembrane 6 and the fluid under pressure in the space or duct 7 isomitted and instead metal tape under tension is helically wound aroundthe membrane 4 as indicated at 8. This layer of metal tape 8 exerts aninward radial force on the impermeable membrane 4 and has the sameeffect as the fluid 7 under pressure P in the cable shown in FIG. 1.

other par- The supertension bushing shown in FIG. 3 has a central metalconductor which is at a high potential, the conductor 10 beingsurrounded by a hollow cylinder 11 of insulating material. An end plate12 is provided at each end of the cylinder 11 and is preferably of aninsulating material. At the inner end and outer edges of the end plates12, seals 13 are provided which engage the central conductor 10 and thecylinder 11. Each end of the conductor 10 is threaded and, at each end,a nut 14 is used to hold a spring member 15 against the end plate 12. Onthe inner side of each of the end plates 12, a corona shield 16surrounds the central conductor 10 and rests against the end plate 12.The corona shield 16 at each end of the bushing is connected to thecentral conductor 10 by a lead 17. An earthed corona shield 18 surroundsthe central part of the conductor 10 and is in the form of a hollowcylinder of sheet metal having a narrow central portion 19 at each endof which there is an outwardly flared portion 20. At each end of theoutwardly flared portion 20 there is provided a further cylindricalportion 21, the outer ends of the cylindrical portions 21 being bentback on themselves as indicated at 22. The ends of the portions 22 arejoined to the hollow cylinder 11 by an impermeable supports 24. Theannular space 25 enclosed by the corona shield 18 and the annularsupports 24 is filled with oil under pressure and contains oil expansionelements 26. The space 27 between the central conductor 10 and thehollow cylinder 11 other than the space 25 is filled with an insulantconsisting of particles of a solid insulating material and oil. A filter28 extends through one of the supports 24 and is permeable to oil butnot to the particles of the solid insulating material. Consequently thepressure of the oil in the space 25 is applied to the insulator in thespace 27 and it will be seen that the insulant in the space 27 ispresent between the corona shield 18, and the central conductor 10. Thecentral conductor 10 is at the high tension whereas the corona shield isearthed and the insulant has been found to operate satisfactorily.

ln all three embodiments, the insulant consists of particles of aninsulating material in a fluid discharge suppressant and it has beenfoundthat this operates satisfactorily. It is believed that the reasonfor the satisfactory operation of the insulant results from the factthat the fluid is effectively in the form of a thin film and when afluid insulant is in the form ofa thin film its specific electricalstrength is increased.

Suitable fluids are, for example, low viscosity mineral oil,fluorocarbon oil, silicone oil, nitrogen and sulphur hexafluoride.Suitable solid insulating materials are, for example, quartz, silica,mica, glass and porcelain which are inorganic materials and polythene,polypropylene, P.T.F.E., P.V.C. and hydrocarbons (e.g. sugar) which areorganic materials. The particle size of the solid insulating material,its compaction and porosity, affect its characteristics.

Suitable materials for use as impermeable membranes are, by way ofexample, lead, aluminum, copper, stainless steel, polyethylene, etc.

The purpose of maintaining interparticle pressure is to inhibit particlemovement and to prevent sedimentation so as to ensure thin filmcondition in the fluid insulant, i.e. the fluid discharge suppressant.

The particles may be of any shape.

I claim:

1. Electrical equipment comprising:

a conductive member; an insulant surrounding said conductive member;said insulant comprising finely divided particles of a solid insulatingmaterial in an insulating fluid, said insulating fluid acting as adischarge suppressant; first pressure applying means for applyingpressure to said insulating fluid to maintain said insulating fluid atabove atmospheric pressure, said first pressure applying means includinga fluid passage means for placing the insulating fluid in fluid flowcommunication with a source of pressurized fluid, said fluid passagemeans being permeable to said insulating fluid and impermeable to saidsolid insulating material; and second pressure applying means forapplying pressure to said solid insulating material to maintaininterparticle pressure to inhibit particle movement and prevent particlesedimentation and thereby maintain the insulating fluid as a thin film.

2. The electrical equipment as claimed in claim 1 and further comprisingan impermeable membrane surrounding the insulant, the insulantsupporting the conductive member in spaced relationship with respect tosaid surrounding impermeable membrane member.

3. The electrical equipment claimed in claim 1 and further comprising animpermeable membrane surrounding the insulant, the second pressureapplying means being in contact with said surrounding impermeablemembrane and applying pressure to the particles through the impermeablemembrane.

4. Electrical equipment as claimed in claim 1 wherein said conductivemember is a stranded hollow conductor, said hollow conductor includingpressurized insulating fluid, said fluid passage means comprising afluid permeable membrane surrounding said conductor, and furthercomprising a first impermeable membrane which surrounds the insulant.

5. Electrical equipment as claimed in claim 4 wherein the secondpressure applying means comprises a second impermeable membrane whichsurrounds and is spaced from the first impermeable membrane, and fluidunder pressure in the space between the first and second impermeablemembranes.

6. Electrical equipment as claimed in claim 4 wherein the secondpressure applying means comprises metal tape under tension wound aroundthe first impermeable membrane.

7. Electrical equipment as claimed in claim 1 in the form of a bushingand further comprising a casing surrounding the conductive member andspaced therefrom, a corona shield of sheet material within the easingwhich surrounds the central part of the conductive member and is spacedtherefrom, said corona shield being secured to the casing and dividingsaid casing into a first space defined by the corona shield and casingand a remaining space, said remaining space containing said insulant,said first pressure applying means comprising insulating fluid underpressure in said first space and said fluid passage means which ispermeable to said insulating fluid and impermeable to said solidinsulating material connecting said first space and remammg space.

8. Electrical equipment as claimed in claim 7 wherein said secondpressure applying means is in contact with said casing and appliespressure to the particles through said casing.

9. Electrical equipment as claimed in claim 1 wherein the solidinsulating material is selected from the group gen and sulphurhexafluoride.

11. Electrical equipment as claimed in claim 1 having at least twoconductive members spaced apart from each other, the space between theconductive members being filled by the insulant.

1. Electrical equipment comprising: a conductive member; an insulantsurrounding said conductive member; said insulant comprising finelydivided particles of a solid insulating material in an insulating fluid,said insulating fluid acting as a discharge suppressant; first pressureapplying means for applying pressure to said insulating fluid tomaintain said insulating fluid at above atmospheric pressure, said firstpressure applying means including a fluid passage means for placing theinsulating fluid in fluid flow communication with a source ofpressurized fluid, said fluid passage means being permeable to saidinsulating fluid and impermeable to said solid insulating material; andsecond pressure applying means for applying pressure to said solidinsulating material to maintain interparticle pressure to inhibitparticle movement and prevent particle sedimentation and therebymaintain the insulating fluid as a thin film.
 2. The electricalequipment as claimed in claim 1 and further comprising an impermeablemembrane surrounding the insulant, the insulant supportiNg theconductive member in spaced relationship with respect to saidsurrounding impermeable membrane member.
 3. The electrical equipmentclaimed in claim 1 and further comprising an impermeable membranesurrounding the insulant, the second pressure applying means being incontact with said surrounding impermeable membrane and applying pressureto the particles through the impermeable membrane.
 4. Electricalequipment as claimed in claim 1 wherein said conductive member is astranded hollow conductor, said hollow conductor including pressurizedinsulating fluid, said fluid passage means comprising a fluid permeablemembrane surrounding said conductor, and further comprising a firstimpermeable membrane which surrounds the insulant.
 5. Electricalequipment as claimed in claim 4 wherein the second pressure applyingmeans comprises a second impermeable membrane which surrounds and isspaced from the first impermeable membrane, and fluid under pressure inthe space between the first and second impermeable membranes. 6.Electrical equipment as claimed in claim 4 wherein the second pressureapplying means comprises metal tape under tension wound around the firstimpermeable membrane.
 7. Electrical equipment as claimed in claim 1 inthe form of a bushing and further comprising a casing surrounding theconductive member and spaced therefrom, a corona shield of sheetmaterial within the casing which surrounds the central part of theconductive member and is spaced therefrom, said corona shield beingsecured to the casing and dividing said casing into a first spacedefined by the corona shield and casing and a remaining space, saidremaining space containing said insulant, said first pressure applyingmeans comprising insulating fluid under pressure in said first space andsaid fluid passage means which is permeable to said insulating fluid andimpermeable to said solid insulating material connecting said firstspace and remaining space.
 8. Electrical equipment as claimed in claim 7wherein said second pressure applying means is in contact with saidcasing and applies pressure to the particles through said casing. 9.Electrical equipment as claimed in claim 1 wherein the solid insulatingmaterial is selected from the group consisting of quartz, fused silica,mica, glass and porcelain.
 10. Electrical equipment as claimed in claim1 wherein said fluid, which acts as a discharge suppressant, is selectedfrom the group consisting of low viscosity mineral oil, fluorocarbonoil, silicone oil, nitrogen and sulphur hexafluoride.
 11. Electricalequipment as claimed in claim 1 having at least two conductive membersspaced apart from each other, the space between the conductive membersbeing filled by the insulant.